Flashcards in Investigation and management of seizures in horses Deck (23):
Ddx - seizures in horses
- fluphenazine toxicity
- narcoplepsy/ sleep deprivation syndrome
- caudal cervical myelopathy (C6-T2)
What causes encephalitis?
not many infectious causes in UK, occasionally EhV-1 but this is usually associated with spinal cord lesions, WNV – flavivirus but rare
Do lyme disease and louping ill affect horses?
- Lyme disease: hard to diagnose but thought to affect horses)
- Louping ill: affects horses in SW
Use of refractometer and CSF analysis
unable to detect protein in CSF as much lower than blood. CSF also has very low cell numbers so needs spinning down, sediment on slide and stained. You can take CSF to normal human hospital for analysis
How may alfalfa hay affect seizuring horses?
high calcium content so possibly neuroprotective to lower seizure threshold
What might you give to a pregnant mare who seizures to maintain the pregnancy?
- Regumate (progesterone analogue to help maintain pregnancy as stress of seizure may cause her to abort)
What might you give to a horse with bacterial meningitis?
- Trimethoprim sulfadiazine BID (probably not necessary but covers in case of bacterial meningitis, one of only Abs that can be given chronically with pregnancy)
Causes of seizures in horses
• Neonatal or congenital
• Secondary – metabolic, Neoplastic, trauma, iatrogenic, (infxn, toxic)
• Primary idiopathic
Types of seizures in horses - 3
- partial (focal, one mm area, usually repeatable),
- generalised (might develop from partial seizure, involve multiple mm groups, might involve loss of consciousness and collapse),
- status epilepticus (loss of consciousness and severe generalised mm contraction spasm with collapse).
Outline seizures in neonatal horses - CS, Tx, prognosis
- CS - Usually dummy foals / foals with NI: ‘chewing gum’ fits, nystagmus, paddling, mimics other problems (especially colic),
- Tx - address primary problems, diazepam or midazolam single dose or infusion.
- Prognosis - Provided primary problems sorted, usually these foals do well.
Outline benign epilepsy of Arabian foals
- Usually cluster seizures at 2-3 months old
- Metabolic evaluation normal. Otherwise normal and foal healthy
- Typically grow out of it by 1-1.5 years old
- Genetic - suggested link with lavender foal syndrome
- Tx - responds to phenobarbitone
What are causes of secondary seizures?
HE (rarely causes seizures, false NTs typically inhibitory so unlikely to cause seizures)
Electrolyte disorders are more common (hypocalcaemia, hypomagnesaemia, hypochloraemia)
o NEOPLASTIC/ SOL: brain tumour and abscess rare in horses, benign SOL = cholesteatoma/ cholesterol granuloma more common. Can obstruct CSF outflow and --> secondary hydrocephalus
o IATROGENIC: air embolism, intra-carotid injections, post-myelography (avoid metrizamide contrast agent as many complications, use iohexol) – tilt horse head during injection of iohexol, premed dexamethasone.
Outline typical clinical pathology of horse with seizures
- Typically normal haematology and Biochem
- Electrolyte disorders may be picked up - underlying hypocalcaemia
- CK often mildly elevated for 24-48 hours post-seizure
- CSF - usually normal, but sometimes inflammatory or degenerative changes
What diagnostic tests can you do for a horse with seizures?
- EEG (electroencephalography) – to confirm partial seizure, unhelpful if you have already have good clinical evidence of seizure activity. Standing or anaesthetised.
- Imaging- radiography rarely beneficial
- Endoscopy, CT/MRI usually without other problems
Emergency tx - seizuring horse
- Very dangerous to tx - only consider if safe and a grand mal seizure is prolonged or there are multiple cluster seizures
- Diazepam (IV or IM)
- Phenobarbitone (dilute in saline IV)
- Pentobarbone (IV to effect, get dose right!!!)
Long term prognosis for a seizuring horse
- Rider safety concern
- If seizure free for at least 6 months, may be appropriate to ride but at their own risk (based on current UK legislation for seizes and driving)
- Only embark on tx if seizures are frequent/ severe
- Phenobarbitone – increase dose 25% every 2 weeks until successful tx. Monitor serum concentrations
- KBr if unacceptable sedation. Monitor serum concentrations.
How do benzodiazepines, phenobarbitone and KBr work?
enhanced GABA activated chloride conductance
How does phenytoin work?
enhanced sodium channel inactivation
What are side effects of anti-seizure drugs?
Side effects in other excitable tissues: cardiac and skeletal mm (arrhythmias and weakness)
Which drugs should you use concurrently with anti-seizure medication? 4
Avoid ivermectin, moxidectin, TCs, acepromazine.
How can you tx seizures in lactating mares?
Phenobarbitone - effective but manage underlying electrolyte disorders. Transferred to foal in milk, can caused sedation. Personal experience and other anecdotal reports suggest that phenobarbitone can be used, at least in late pregnancy, and during lactation.
Prognosis - seizuring horses
- very variable
- some horses with inflammatory CSF respond rapidly and don't require long term anti-seizure medication
- Some horses can be taken off medication after 6 months (but might relapse) - reduce medication slowly over several weeks
- Some horses don't respond or owners run out of money and horse requires euthanasia
- Some owners of competition horses elect to continue without any tx